Information for systems, such as data processing systems is typically stored on storage media, such as magnetic disks. In manufacturing disks, a disk drive having a number of internal heads is typically mounted in a mastering station referred to as a servo-writer. The servo-writer has sensors positioned outside of the disk drive to locate the radial and circumferential position of at least one of the heads, such that a pattern of magnetic information may be written onto the disk surface coupled to the writing head. The pattern becomes the master reference used by the disk drive during normal operation to locate the tracks and sectors for data storage.
The process of servo writing on a station is expensive as each disk drive must be serially mounted in the servo-writer. In addition, the mechanical boundary conditions of the disk are altered as sensors must have access to the actuator and the disk spindle motor. This can require mechanical clamping and disassembly of the file.
One process for writing servo information is described in U.S. Pat. No. 4,414,589, entitled "Embedded Servo Track Following System and Method for Writing Servo Tracks" issued on Nov. 8, 1983 and assigned to Northern Telecom, Inc. In U.S. Pat. No. 4,414,589, a servo track following system for positioning a moving read/write head relative to a magnetic storage disk is described. A plurality of servo tracks are recorded in sectors on the disk for identifying radial positions or informational tracks. A clock track is written by writing a single pulse on a fixed clock track head, phase-lock looping to an intermediate clock track, which is written on a moving head, and then phase-lock looping up to the final clock track, which is written on the fixed clock track head. Radial track density is then determined by moving a head to a limit stop and writing a reference track. Thereafter, the head is displaced an amount sufficient to reduce the amplitude of the reference track by a predetermined percentage which is related to the ultimate average track density. Thereafter, another reference track is written and the head is again stepped away from the second reference track an amount sufficient to again reduce the amplitude of the reference track by a predetermined percentage. This is continued until the disk is filled with reference tracks. If the average track density thus achieved is unsatisfactory, the reduction number is adjusted and the process is repeated.
Another technique for writing servo information is described in U.S. Pat. No. 4,531,167, entitled "System for Magnetic Disk Drives" issued on Jul. 23, 1985 and assigned to Pioneer Research, Inc. In U.S. Pat. No. 4,531,167, before servo tracks are written on a disk, it is first necessary to write a master clock track on the disk by a separate head, which serves as a timing reference for the entire operation. Servo bursts are then written on the disk by writing EVEN servo information over the entire surface of the disk. This is achieved by first moving the arm to the outer crash stop and then causing the arm to move radially a distance less than a data track width for each revolution of the disk. Thereafter, the arm is again driven against the outer crash stop and the head is caused to write ODD servo information in a number of sectors of the disk drive. After the arm used in writing the ODD servo information reaches the inner diameter of the disk, a comparison of the number of steps it takes the arm to proceed from the outer crash stop to the inner crash stop is made with the number of tracks actually required on the disk. If the number of actual steps is different from the number of tracks actually required, a particular bias, of an amount determined by the microprocessor, will be introduced so that on the next operation the number of steps will exactly equal the number of tracks required on the disk.
Each of the above procedures requires an external timing sensor in order to write timing patterns used in determining the circumferential position of the heads. Further, since external sensors are needed, a clean room environment is necessary. In addition, in order to determine the track pitch which is later used to write a servo-pattern, an entire disk of information is written. This is time consuming and expensive. Therefore, a need exists for a technique for writing servo-patterns on a disk which does not require a clean room environment. In addition, a need exists for a technique for writing servo-patterns such that no external sensors are needed. Yet another need exists for a method for determining which head writes the widest track in a recording device. Also, a need exists for a method for determining the track pitch of a recording device without writing a full disk of information. Further, a need exists for a technique for writing timing information in which an external clock source is eliminated, thus reducing the possibility of error arising from relative motion between the head that is writing the servo-pattern and the clock source.